Transmission line hangers are used to support transmission lines. Generally, a transmission line is inserted into a transmission line hanger which is then attached to a supporting structure. The most extensive use of hangers is in connection with coaxial cables, such as those disclosed in U.S. Pat. No. 5,334,051 to Devine et al. and U.S. Pat. No. 5,167,533 to Rauwolf. Coaxial cables are extensively used for carrying a variety of electromagnetic signals. In most uses, the cables need to be attached to a supporting structure along most of their lengths.
Transmission line hangers are also used for supporting waveguides which carry electromagnetic signals from transmitting or receiving equipment in an equipment shelter to an antenna mounted on a tall tower. A large number of hangers are required to support a waveguide beneath a horizontal waveguide bridge extending between the shelter and the base of the tower and to support the waveguide on the tower as the waveguide extends upwardly to the antenna. An even larger number of hangers are required where separate waveguides extend to several antennas on a signal tower. Commercially available waveguides have a variety of cross-sectional shapes. For example, a variety of waveguide shapes are disclosed in U.S. Pat. No. 3,822,411 to Merle and U.S. Pat. No. 4,047,133 to Merle.
Typically, transmission line hangers are attached to a supporting structure, such as a transmission line bridge or an antenna tower, by inserting a bolt through a U-shaped hanger and through a hole in the supporting structure. The bolt is held in place by a nut and lock washer. After the hangers have been attached to the supporting structure, the transmission line is strung along the bridge, up the tower, and clamped between the legs of each U-shaped hanger by tightening a clamping screw which extends between the legs. A considerable amount of installation time is required, first to attach the large number of hangers to the bridge and the tower and then to clamp the transmission line within the hangers. In addition, a large amount of auxiliary hardware (e.g., screws, bolts, nuts, and washers) is required, along with the hangers themselves.
A spring hanger system for supporting a VHF circular waveguide is disclosed in U.S. Pat. No. 4,654,612 to Smith. A variety of prior hangers for microwave transmission lines are disclosed in Andrew Corporation Catalog #36. An improved waveguide hanger is disclosed in U.S. Pat. No. 4,763,132 to Juds et al. The waveguide hanger disclosed therein is in the form of a resiliently yieldable and generally U-shaped clip that is adapted to be slipped over an elliptical waveguide and snapped into a supporting structure. The clip includes a hinge portion that extends between the legs of the clip.
Another cable hanger is disclosed in U.S. Pat. No. 5,393,021 to Nelson. The cable hanger disclosed therein includes a hinge section, a cable retention section, and a structure attachment section having two locking members that each include a pair of concave locking barbs. Cable hangers that include a hinge section can only accommodate a limited range of cable diameters. The maximum cable diameter accepted by such cable hangers is limited by the maximum circumference of the cable retention section.
Prior transmission line hangers, such as those disclosed in Nelson and Juds et al., also place the cable retention section close to the attachment section. Thus, the attachment section is traditionally short in length. This makes the attachment section rigid and non-compliant which makes installation of such hangers difficult, especially where a large diameter cable is being installed on a tower or where the weather conditions limit manual dexterity, e.g., cold weather. In such situations, tools may be required to squeeze the hanger into the tower aperture. The use of tools is undesirable, especially where a transmission line is being installed on a tall tower.
Furthermore, some prior hanger designs do not adequately prevent longitudinal movement of the cable with respect to the hangers. Hangers without mechanisms for penetrating or biting into the cable jacket cannot prevent longitudinal movement of the cable because the frictional coefficient between the metal hanger and the plastic cable jacket is very low. The polyethylene typically used for cable jackets is a soft material that has an inherent lubricant quality. In addition, the cable jacket can “cold flow” which reduces the holding force of the cable hanger over time, resulting in cable slippage.
Moreover, due to the increasing number of antennas being installed on antenna towers, multiple transmission lines must be strung along the tower to connect to those antennas. Therefore, hangers capable of supporting a plurality of parallel transmission lines were developed. One such example is U.S. Pat. No. 5,794,897 to Jobin et al. This patent discloses a two piece transmission line hanger that is stackable to accommodate a plurality of parallel transmission lines.
One drawback of current stackable hanger designs, however, is that a considerable amount of installation time is required to attach the two hanger halves around the transmission line(s) and the hanger assembly to the supporting structure. In addition, auxiliary hardware (e.g., screws, bolts, nuts, and washers) is required to secure the hangers to the supporting structure. Moreover, when subsequent transmission lines must be added to accommodate one or more new antennas, the existing two piece stackable hanger assembly has to be unassembled to add another hanger thereto. For instance, the bolt of the first hanger has to be removed, the two hanger halves of another hanger must be placed around the new transmission line(s) and the four hanger halves must be assembled together by inserting a bolt through the hangers and through a hole in the supporting structure and fastening a lock washer and a nut to the bolt. Therefore, there is a need for a novel stackable transmission line hanger that is easy to install, easy to add additional transmission lines thereto, and inexpensive to manufacture.
The installation of one or more transmission lines along a supporting structure is often a difficult and time-consuming operation because of the large amount of auxiliary hardware required to install some prior hangers and/or the necessity to remove an assembled hanger to add an additional transmission line. Therefore, there is a continuing need for easy to install stackable hangers and for improved methods of installing them. The present invention addresses these needs by providing a one piece, stackable transmission line hanger capable of securing one or more transmission lines. The stackable hanger is expandable to accommodate additional transmission lines without unassembling the prior hanger(s), is expandable to accommodate a large number of transmission line diameters, is inexpensive to produce, and is quickly and easily installed. In addition, the stackable hanger reduces the number of components required to secure one or more transmission lines, reduces installation time, reduces longitudinal movement of the transmission line within each hanger, and allows for simple installation of additional transmission lines.
While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.